Aluminum-Containing SBA-15 as Cracking Catalyst for the Production

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Microporous and Mesoporous Materials 102 (2007) 310–317

Aluminum-containing SBA-15 as cracking catalyst for the productionof biofuel from waste used palm oil

Yean-Sang Ooi, Subhash Bhatia *

School of Chemical Engineering, University Science of Malaysia, Engineering Campus, 14300 Nibong Tebal, S.P.S Penang, Malaysia

Received 10 September 2005; received in revised form 7 November 2006; accepted 30 December 2006Available online 8 January 2007

Abstract

Aluminum-containing SBA-15 mesoporous materials were prepared using two different methods in order to compare their crackingactivity in gasoline production from waste used palm oil. The catalyst prepared via direct synthesis (AlSBA) possessed disorder pore sizedistribution whereas the catalyst prepared via post-synthesis (ACSBA) had narrow pore size distribution. Both the catalysts gave com-parable activity but regenerated ACSBA exhibited higher activity and yield of gasoline fraction as compared to AlSBA. This could beattributed due to the better thermal stability of ACSBA.� 2007 Elsevier Inc. All rights reserved.

Keywords: Aluminum-containing SBA-15; Catalytic cracking; Biofuel; Waste used palm oil

1. Introduction

New type of ordered porous materials with combinedmicro- and mesopores are widely studied by the researchersdue to their significant supplementary advantages [1]. SBA-15 is by far the largest mesoporous material with highlyordered hexagonally arranged mesopores, thick wall andthus with better thermal and hydrothermal stability. Ithas micropores that are created by the penetration of thehydrophilic poly(ethylene oxide) chain from triblock sur-factant into the silica walls [1]. The template used for thesynthesis of SBA-15 is relatively cheap, nontoxic and bio-degradable as compared to others organic directing agentsused in the preparation of MCM-41 [2,3]. This has stimu-lated the researchers to further improve its chemical andphysical properties so that it can be used as a catalyst forthe industrial processes.

However, the pure siliceous SBA-15 does not possessany kind of acidity and therefore its application as a cata-lyst is limited. The introduction of aluminum in the frame-

1387-1811/$ - see front matter � 2007 Elsevier Inc. All rights reserved.

doi:10.1016/j.micromeso.2006.12.044

* Corresponding author. Tel.: +60 4 599 6409; fax: +60 4 594 1013.E-mail address: [email protected] (S. Bhatia).

work of SBA-15 to create the desired acidity has receivedconsiderable attention [4–6]. This is due to the increasingimportance of the large molecules especially in catalyticupgrading of heavy oils [7]. The strong acidic synthesis con-ditions generally are not favorable for the direct incorpora-tion of aluminum into SBA-15 [6]; therefore differentmethods have been reported in the literature for the intro-duction of aluminum in SBA-15 [4–6]. Yue et al. [4] haveutilized aluminum tri-tert-butoxide as aluminum sourceand successively incorporated aluminum in the frameworkof SBA-15. Whereas, Vinu et al. [5] used aluminum iso-propoxide as aluminum source in direct synthesis ofAlSBA-15 with Si/Al ratio up to 7. Han et al. [6] effectivelyintroduced aluminum in SBA-15 by a two-step procedurewhere the first precursor contained zeolite nanoclustersand the second preformed precursor assembled with the tri-block copolymers in strong acidic media. The aluminumincorporated in the framework of the zeolite nanoclusterswas introduced into the mesoporous structure without con-tinuous growth into larger crystals, due to the strong acidicconditions.

The cracking activity of direct synthesis AlSBA-15 hasbeen investigated for the production of biofuel from wastefatty acids mixture in our previous work [8]. It will be

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Y.-S. Ooi, S. Bhatia / Microporous and Mesoporous Materials 102 (2007) 310–317 311

interesting to compare the catalytic properties of alumi-num-containing SBA-15 prepared via post-synthesismethod and direct synthesis. The cracking activity of theAlSBA-15 prepared is tested for biofuel production fromwaste used palm oil. The preparation method using post-synthesis strategy is found to produce catalysts withcomparable acidity. In the present research, the catalyticactivity of two types of aluminum-containing SBA-15 iscompared for the cracking of waste used palm oil. Theactivity of the regenerated catalyst is also compared withthe fresh catalyst’s activity.

2. Experimental

2.1. Catalyst preparation

2.1.1. SBA-15 and AlSBA-15

SBA-15 and AlSBA-15 were prepared following the pro-cedure reported in the literature [2,4]. 9.8 g of triblockcopolymer poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) (Aldrich, average molecularweight = 5800) was dissolved with stirring in 313 ml ofdeionized water and 40 ml of hydrochloric acid (37 wt.%)for 1 h at 323 K. Subsequently, 21.7 g of tetraethylortho-silicate (Merck, TEOS) was added and stirred for another10 min. The mixture was heated at 333 K for 24 h and thenat 373 K for another 24 h in a Teflon container understirring. The triblock copolymer was removed upon calci-nation at 823 K for 6 h. Al-containing SBA-15 was synthe-sized using the same method as mentioned above but anappropriate amount of Al(O-sec-Bu)3 (Merck) was firstdissolved with TEOS in 20 ml of HCl solution for 3 h prioradding in to the triblock copolymer solution. The Al-containing SBA-15 was denoted as AlSBA(X) where X isthe Si/Al ratio (5, 10 and 20).

2.1.2. Post-treatment of SBA-15

Four grams of SBA-15 was dispersed in 100 ml solutionof AlCl3 (Fluka) and refluxed at 353 K with stirring for 2 h.The aluminum-containing mesoporous material was fil-tered and thoroughly washed with deionized water untilit is free of Cl� ions. The powder was dried at room tem-perature and calcined at 823 K for 4 h. The materials weredesignated as ACSBA(X) where C is denoted to the chlo-ride form of the aluminum source, and X is the Si/Al ratio(5, 10 and 20 with the amount of AlCl3 added as 1.76 g,0.88 g and 0.44 g, respectively).

2.2. Characterization

The BET surface area and pore size distribution of thecatalysts were measured by nitrogen adsorption using anAutosorb I (Quanta chrome Automated Gas Sorption Sys-tem). The total pore volume was estimated from the des-orbed amount at relative pressure of 0.90. Mesoporositywas calculated from the desorption branch using the BJHmethod. The BJH pore size was defined as the position of

the maximum peak on the BJH pore size distribution.The samples were degassed for 5 h under vacuum at573 K (for fresh catalysts) or 393 K (for deactivated cata-lysts) prior to the analysis. The nature of the acid sites pres-ent in the SBA-15 was determined using FTIR technique.The sample was exposed to excess pyridine for 1 h afterdegassing at 473 K, followed by desorption of physicallyadsorbed pyridine at 423 K under vacuum. The IR spectrawere scanned using a Perkin–Elmer FTIR (Model 2000) inthe range of 1400–1700 cm�1. Transmission electronmicroscopy (TEM) was performed with a Philips CM12Transmission Electron Microscope operated at 80 kV.

2.3. Activity test

The cracking activity of the catalysts was measured atreaction temperature of 723 K and a feed rate of waste usedpalm oil (weight hourly space velocity, WHSV) of 2.5 h�1 atatmospheric pressure in a fixed-bed micro-reactor rigreported elsewhere [9]. 0.5 g of catalyst in the form of pow-der was loaded over 0.2 g of quartz wool supported by astainless steel mesh in the micro-reactor (185 mm · 10 mmID) placed in the vertical tube furnace (Model No. MTF10/25/130, Carbolite, UK). The liquid product was col-lected in a glass liquid sampler, while the gaseous productswere collected in a gas-sampling bulb, once the steady statewas reached in the reactor. The unconverted oil was sepa-rated from the liquid product by distillation in a micro-dis-tillation unit (Buchi B850, GKR) at 473 K for 30 min undervacuum (100 Pa) with the pitch as the residual oil. The gas-eous products were analyzed over a gas chromatograph(Hewlett Packard, Model 5890 series II) using a HP PlotQ capillary column (divinyl benzene/styrene porous poly-mer, 30 m long · 0.53 mm ID · 40 lm film thickness)equipped with a thermal conductivity detector (TCD) andnitrogen as a carrier gas. The organic liquid product(OLP) was analyzed using a capillary glass column (Petro-col DH 50.2, film thickness 0.5 lm, 50 m long · 0.2 mmID) at a split ratio of 1:100, using a FID detector. The com-position of OLP was defined according to the boiling rangeof petroleum products in three categories i.e. gasoline frac-tion (333–393 K), kerosene fraction (393–453 K) and dieselfraction (453–473 K). The spent catalyst was washed withacetone prior to the coke analysis. The amount of cokewas determined by the difference in weight before and aftercalcination in muffle furnace. The catalyst regenerated bycalcination in muffle furnace was tested also for its crackingactivity. The nature of the coke was studied using TGAanalysis at a heating rate of 10 K/min, from 373 K to973 K under a flow of oxygen gas.

3. Results and discussion

3.1. Catalyst characterization

The nitrogen adsorption-desorption data of SBA-15materials are given in Table 1. The BET surface area of

Table 1Nitrogen adsorption–desorption data for as-calcined SBA-15 materials

Catalyst BET surface area(m2/g)

Pore volume(cm3/g)

Average pore size(nm)

SBA-15 676 1.05 6.0AlSBA(5) 619 0.60 –AlSBA(10) 705 0.66 –AlSBA(20) 728 0.99 8.6ACSBA(5) 557 0.73 6.1ACSBA(10) 491 0.66 6.1ACSBA(20) 529 0.70 6.1

312 Y.-S. Ooi, S. Bhatia / Microporous and Mesoporous Materials 102 (2007) 310–317

SBA-15 was 676 m2/g with the total pore volume of1.05 cm3/g and 6.0 nm pore size. By addition of aluminumvia direct synthesis, the BET surface area increased to728 m2/g for AlSBA(20) and 705 m2/g for AlSBA(10),respectively. However, high loading of aluminum wasaccompanied by a drop in the BET surface area to619 m2/g for AlSBA(5). This phenomenon was due to thegradual loss of pore network ordering, which could benoticed from the nitrogen adsorption isotherm illustrated

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Fig. 1. Isotherms of nitrogen sorption for aluminum-containing SBA-15prepared via (a) in situ method and (b) post-treatment.

in Fig. 1a. The capillary condensation step on the nitrogenadsorption isotherm was found to be broad, indicating awide range of pore sizes, as confirmed by the BJH pore sizedistribution (Fig. 2). It is interesting to note that the poresize of AlSBA(20) increased to 8.6 nm as compared toSBA-15. This may be due to the presence of aluminum inthe silica walls [5]. In case of Si/Al ratio lower than 20,the materials showed the loss of the organized structurewith the emergence of secondary pore size. The isothermsof AlSBA(10) and AlSBA(5) indicated that these materialshave regular cylindrical mesopore system with the blockedopenings [1]. This could be observed from the desorptionbranch of the isotherms and the shape of the hysteresisloop, which corresponds to ink-bottle pores. This maydue to the presence of aluminum oxide species. The highloading of aluminum was hindered for direct synthesisdue to the pore blockage and disorder pore structure ofthe material.

Introduction of aluminum using post-synthesis pro-duced mesoporous materials with lower BET surface areain the range of 491–557 m2/g, which was due to the loadingof aluminum into the micropores. This was observed fromthe decrease in the pore volume but retained the BJH pore

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Fig. 2. Pore size distribution of SBA-15 compared with Al-containingSBA-15 prepared via (a) in situ method and (b) post-treatment.

Fig. 3. TEM images of (a) SBA-15, (b) AlSBA(5) and (c) ACSBA(5).

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1446

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1542

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ecnabrosbA

Fig. 4. FT-IR spectra for the pyridine-adsorbed: (a) SBA-15, (b)ACSBA(5), (c) AlSBA(10), (d) ACSBA(20), (e) AlSBA(5), (f) ACSBA(10)and (g) AlSBA(20).


size with identical pore size distribution after post-treat-ment. It can be observed from Fig. 1b that the isothermsof post-treated SBA-15 exhibited similar shape and hyster-esis to that of SBA-15 except with lower adsorbed volumeinto intra-wall micropores (occurred at low relative pres-sures). When the material of low Si/Al ratio of 5 was pre-pared, the coverage of the aluminum started to grow alongthe mesopore and resulted in a narrower pore size distribu-tion compared to SBA-15 (Fig. 2b). The slightly higherloading of aluminum was also confirmed by the lower Si/Al content of ACSBA(5) as compared to ACSBA(10)and ACSBA(20). The adsorption in much larger poreswhere capillary condensation took place at relative pres-sures above 0.9 corresponds to secondary mesoporosity,such as interparticle voids [7]. The unchanged capillarycondensation at relative pressure higher than 0.9, indicat-ing that no aluminum was accommodated at the externalsurface of post-treated SBA-15. Therefore, post-treatmentgave the advantages of retaining the organized pore struc-ture, yet enabling the introduction of high amount of alu-minum in SBA-15, which was difficult in the directsynthesis method.

Fig. 3 shows the TEM images of the representative sam-ples of SBA-15, AlSBA(5) and ACSBA(5). The mesoporesin SBA-15 and post-treated SBA-15 (ACSBA(5)) runsmoothly over several micron of length with open meso-pore, whereas AlSBA(5) displays some blockage and disor-der in the pore openings. A comparatively thicker wall(around 6.0–10.0 nm) for both the aluminum-containingSBA-15 was observed as compared to SBA-15. The thickerwall gave raise to the volume of micropores in AlSBA(5),which can be further confirmed from the pore size distribu-tion (Fig. 2). The post-synthesis method loaded aluminumin the intra-wall micropores and along the inner surface ofthe mesopore and micropore; hence ACSBA(5) possessesmuch dense and uniform pore wall with regular porestructure.

In order to identify the nature of the active sites (Lewisand Brønsted acid sites) present in the mesoporous materi-als prepared, FTIR spectra of the pyridine absorbed regionwere obtained and the results are shown in Fig. 4. Themesoporous materials show the bands associated with thecombination of Lewis and Brønsted acidities (1490 cm�1),hydrogen-bonding (1446 cm�1; 1600 cm�1) and strongBrønsted acidity (1542 cm�1 and 1638 cm�1) [10]. StrongBrønsted acid site at the band of 1542 cm�1 only existedin SBA-15 with Si/Al ratio 5. AlSBA(10) depicted lowintensity for hydrogen-bonding band which could be dueto the disorder pore structure and therefore prohibitedthe accessibility of the hydroxyl group. Similarly, thehydrogen-bonding at 1446 cm�1 and 1600 cm�1 diminishedupon high loading of aluminum via post-synthesis, indicat-ing that the loading process occurred at the hydroxylgroup. However, it was shown that intensity of the bandat 1446 cm�1 and 1600 cm�1 for ACSBA(20) was retained,suggesting that the high concentration of hydroxyl groupin SBA-15.


3.2. Catalytic cracking

The conversion of waste used palm oil over SBA-15 andAlSBA are presented in Fig. 5a. The cracking productswere mainly organic liquid product (OLP), gaseous prod-uct, water and coke. The conversion of waste used palmoil and yield of product are defined as:

Conversion ðwt:%Þ

¼ ½gas ðgÞ þOLP ðgÞ þ water ðgÞ þ coke ðgÞ�used palm oil feed ðgÞ � 100 ð1Þ

Yield ðwt:%Þ ¼ desired product ðgÞused palm oil feed ðgÞ � 100 ð2Þ

The conversion of waste used palm oil decreased with timeon stream (TOS) due to the coke formation and its deposi-tion on the catalyst surface and the pore blockage ofmicropores in the intra-wall. The activity of the alumi-num-containing SBA-15 deactivated at a lower rate thanSBA-15 except AlSBA(10). It can be explained from thelow acidity as discussed in FTIR analysis and inaccessibil-ity of acid sites in AlSBA (10) due to the disorder pore

Fig. 5. Effect of the time on stream and regeneration for the conversion ofwaste used palm oil cracking over SBA-15, aluminum-containing SBA-15prepared via in situ method and post- treatment of SBA-15.

structure. The conversion of AlSBA(10) in waste used palmoil cracking was the lowest among the catalysts used and itdeactivated after 5 h of reaction time and gave a conversionof only 50 wt.%. SBA-15 deactivated at the faster rate after5 h of TOS due to its weak acidity. Nevertheless, the exis-tence of hydroxyl groups enable SBA-15 to be more activethan AlSBA(10) at low TOS before the conversion overboth the catalysts dropped to the same level at the endof the first cycle of reaction. After calcination in air,AlSBA(10) gave a higher conversion (59–72 wt.%) as com-pared to the regenerated SBA-15 but slightly lower thanthe fresh catalyst (52 wt.% to 75 wt.%). This could be dueto the loss of hydroxyl groups in SBA-15 during the calci-nation. AlSBA(5) and AlSBA(20) show almost identicaltrend of conversion but with 10 wt.% interval due to thedifference in aluminum content and acidity. AlSBA(5) withhigher aluminum loading gave the conversion in the rangeof 75–96 wt.% during 6.4 h TOS whereas AlSBA(20) gavethe conversion in the range of 68–86 wt%. After regenera-tion, the catalyst still gave high activity in waste used palmoil cracking but with lower activity as compared to thefresh catalyst. The rate of deactivation was faster for regen-erated AlSBA(5) and AlSBA(20) but became constant asthe TOS reached 11 h. This behavior indicated that the cat-alytic properties changed after the regeneration due to thethermal condition during the coke combustion. The BETsurface area and pore properties of the regenerated catalystafter second cycle of reaction are given in Table 2. It can beseen from the table that the BET surface area and pore vol-ume decreased accordingly. Secondary pores were also gen-erated in the ACSBA catalysts with an average pore size of2.3 nm. This could probably due to the destruction of thecatalyst structure after thermal treatment and hence af-fected the catalytic activity.

Aluminum-containing SBA-15 prepared via post-syn-thesis exhibited a more significant effect of TOS in termof conversion (Fig. 5b). All the catalysts gave high conver-sion at initial stage of the cracking reaction (more than90 wt.%); however, the rapid catalyst deactivation wasobserved. The fast deactivation rate could be attributedto the rapid pore blockage of the catalysts and hence theaccessibility to the active sites was prohibited. ACSBA(5)with the growth of aluminum along the mesopore resultedin a narrower pore size distribution gave the fastest deacti-

Table 2Nitrogen adsorption–desorption data for regenerated SBA-15 materials

Catalyst BET surface area(m2/g)

Pore volume(cm3/g)

Average pore size(nm)a

SBA-15 464 0.78 5.2(2.3)AlSBA(5) 577 0.62 5.8(2.8)AlSBA(10) 560 0.58 5.6(2.8)AlSBA(20) 542 0.76 5.2ACSBA(5) 429 0.59 4.6(2.3)ACSBA(10) 374 0.56 4.5(2.3)ACSBA(20) 453 0.60 5.2(2.3)

a Secondary pore size is given in parentheses.

Fig. 6. Effect of the time on stream and regeneration for the gasolinefraction yield of waste used palm oil cracking over SBA-15, aluminum-containing SBA-15 prepared via in situ method and post- treatment ofSBA-15.


vation rate. Nevertheless, the catalysts recovered its activityand showed nearly the same trend of activity as that of thefirst cycle of reaction after regeneration. The end of secondcycle gave the conversion over ACSBA catalysts in therange of 70–80 wt.%, which was higher than AlSBA cata-lysts (in the range of 60–70 wt.%). This shows that the alu-minum introduced via post-synthesis method offered amore stable catalyst in terms of cracking activity.

In order to determine the deactivation rate of the cata-lysts, a deactivation model is proposed by assuming thatthe catalyst activity (u) is dependent on the time on stream(TOS), t. The rate of deactivation is presented as:

dudt¼ �kdu

nd ð3Þ

where u is the catalyst activity, kd is the deactivation rateconstant (h�1) and nd is the order of catalyst deactivation.The value for kd and nd were estimated from Eq. (3) usingnon-linear regression analysis method based on Leven-berg–Marquard’s algorithm [11]. Table 3 presents the valueof kd and nd for different catalysts. Pure silica SBA-15 gavethe highest value of deactivation rate constant and order ofcatalyst deactivation. This was due to the lack of acid sitesin SBA-15 and deactivated at the fastest rate. AlSBA cata-lysts deactivated at a lower rate than ACSBA catalysts andthe difference in the values of deactivation rate constantand deactivation order can be observed in Table 3.

Despite of the conversion, the yield of desired product,gasoline fraction, was the main concern in determiningthe most efficient catalyst. Fig. 6 shows the reaction timedependency for the yield of gasoline fraction over variouscatalysts. There was no correlation between the yield ofgasoline fraction with the conversion especially in the firstcycle of the reaction, and the gasoline yield decreased withTOS. This phenomenon is common in cracking process dueto the catalyst deactivation and dropping in further crack-ing towards lighter products. The yield of gasoline fractionwas higher over the catalyst with lower Si/Al ratio as moreacid sites were available for cracking reaction to occur.AlSBA(5) gave gasoline fraction yield as 40 wt.% at thebeginning of the reaction time. The gasoline yield droppedto 23 wt.% after 6.4 h of TOS, since the catalyst was deac-tivated and more coke was deposited at the active sites.SBA-15 gave a maximum gasoline yield of 28 wt.% at4.8 h TOS but dropped to the lowest gasoline yield of

Table 3Deactivation rate constant, kd and deactivation order, n for differentcatalysts

Catalyst kd n

SBA-15 0.2580 2.7AlSBA(5) 0.0808 1.1AlSBA(10) 0.1750 1.2AlSBA(20) 0.1010 1.7ACSBA(5) 0.1677 2.2ACSBA(10) 0.1825 1.8ACSBA(20) 0.1136 1.0

12 wt.%. This revealed that the strength of acidity playedan important role in gasoline production. This wasreported in the cracking of paraffin where the productchain length was dependent on the strength of the Brønstedsites [12]. After regeneration, the gasoline yield as well asconversion decreased due to the changes in the catalyststructure. Unlike direct synthesis AlSBA catalysts, ACSBAcatalysts also gave lower gasoline yield by following thetrend of its conversion for both the fresh and regeneratedcatalysts. On the other hand, the overall yield of gasolineover ACSBA catalysts was higher than AlSBA catalysts.The regenerated catalysts also gave high yield of gasolineespecially in the initial stage of reaction. This again con-firmed that the post-synthesis catalysts exhibited more reli-able activity and selectivity toward biofuel production.

Coke cannot be considered as an inert with respect tothe cracking reactions, as their formation could stronglyinfluence the catalyst performance. Two possible deactiva-tion modes were considered (1) active site poisoning bycoke coverage; (2) inaccessibility of the reactants due to

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pore blockage [13]. In order to understand the coke depo-sition and the type of coke formed, the deactivated cata-lysts were further characterized by TGA analysis andnitrogen adsorption-desorption. Fig. 7 shows the weightloss of the coked catalysts SBA-15, AlSBA-15 andACSBA(5) after the first cycle of cracking reaction. TheTGA analysis of the aluminum-containing SBA-15 exhib-ited comparable profile with two distinct weight losses atidentical temperature range. The coke content was highfor both the catalysts, which comprised almost 60 wt.%of the total weight of the deactivated catalysts. WhereasSBA-15 exhibited lower content of coke formation withonly 30 wt.% of the total weight of deactivated catalyst.This was in agreement that cracking reaction generallyoccurred on the catalyst acid sites and precoke speciesare made available on the active site [12]. However, theopen structure of SBA-15 eased the deposition of coke pre-cursor and resulted in high coke content as compared tothe microporous catalyst. The high coking was not onlydue to low silica–alumina ratio but also could be due tothe geometrical freedom which enabled the formation oflarge polynuclear hydrocarbon. The BET surface area ofdeactivated catalysts dropped to zero especially for cata-lysts with low Si/Al ratio, while the BET surface area ofSBA-15 was only 98 m2/g at the end of first reaction cycle.The micropores were blocked with coke for all the catalystssince no microporosity was detected from the nitrogenadsorption-desorption analysis. It is probable that thesevere coking of the catalysts started from internal poremouth plugging. Fig. 8 compares the derivative weightcurve of the selected coked catalysts after the first and sec-ond cycle of the cracking reaction. The derivative weightcurves gave two peaks in the range of 573–673 K and723–873 K that corresponded to the soft and hard coke,respectively. SBA-15 with low acidity exhibited low inten-sity of the peaks as compared to the aluminum-containingSBA-15. The regenerated SBA-15 gave higher yield of softcoke while regenerated aluminum-containing SBA-15 showweak intensity for both the peaks. This suggests that thecatalysts structure or the acidic properties can be partly

Fig. 7. TGA analysis of coke for SBA-15, AlSBA(5) and ACSBA (5) afterthe first cycle of the cracking reaction.

Fig. 8. Derivative weight curves for the coke analysis of fresh catalystsand regenerated catalysts after cracking process.

changed due to coking during the cracking reaction or dur-ing the thermal treatment of regeneration process.

4. Conclusions

Aluminum-containing SBA-15 prepared via post-syn-thesis enabled the production of catalysts with low silica–alumina ratio without altering their pore size distribution.Yet these catalysts have shown comparable activity withthe catalysts prepared via direct synthesis in the used palmoil cracking. Furthermore, the regenerated ACSBA cata-lysts gave better activity and yield of gasoline fraction thanAlSBA catalysts, even though the pore structure changeddue to coking and regeneration steps.


Acknowledgments

The authors would like to acknowledge the researchgrant provided by the Ministry of Science, Technologyand Environment, Malaysia under long term IRPA grant(Project: 02-02-05-2184 EA005), that has resulted in thisarticle.

References

[1] P. van der Voort, P.I. Ravikovitch, K.P. de Jong, M. Benjelloun, E.van Bavel, A.H. Janssen, A.V. Neimark, B.M. Weckhuysen, E.F.Vansant, J. Phys. Chem. B 106 (2002) 5873.

[2] D. Zhao, J. Feng, Q. Huo, N. Melosh, G.H. Fredrickson, B.F.Chmelka, G.D. Stucky, Science 279 (1998) 548.

[3] D. Zhao, Q. Huo, J. Feng, B.F. Chmelka, G.D. Stucky, J. Am. Chem.Soc. 120 (1998) 6024.

[4] Y.-H. Yue, A. Gedeon, J.-L. Bonardet, J.B. d’Espinose, N. Melosh, J.Fraissard, in: A. Sayari, M. Jaroniec, T.J. Pinnavaia (Eds.), Studieson Surface Science Catalysis, vol. 129, Elsevier, Amsterdam, 2000, p.209.

[5] A. Vinu, V. Murugesan, W. Bohlmann, M. Hartmann, J. Phys.Chem. B 108 (2004) 11496.

[6] Y. Han, F.-S. Xiao, S. Wu, Y. Sun, X. Meng, D. Li, S. Lin, F. Deng,X. Ai, J. Phys. Chem. B 105 (2001) 7963.

[7] E. Byambajav, Y. Ohtsuka, Appl. Catal. A 252 (2003) 193.[8] Y.-S. Ooi, R. Zakaria, A.R. Mohamed, S. Bhatia, Catal. Commun. 5

(2004) 441.[9] Y.-S. Ooi, R. Zakaria, A.R. Mohamed, S. Bhatia, Biomass and

Bioenergy 27 (2004) 477.[10] B. Chakraborty, B. Viswanathan, Catal. Today 49 (1999) 253.[11] J. Ancheyta-Juarez, F. Lopez-Isunza, E. Aguilar-Rodriguez, J.C.

Moreno-Mayorga, Ind. Eng. Chem. Res. 36 (1997) 5170.[12] K.A. Cumming, B.W. Wojciechowski, Catal. Rev. – Sci. Eng. 38

(1996) 101.[13] M. Guisnet, P. Magnoux, Stud. Surf. Sci. Catal. 88 (1994) 53.

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Aluminum-Containing SBA-15 as Cracking Catalyst for the Production